The present invention is generally directed to a dual-chamber implantable cardiac defibrillator (ICD), system and method. The present invention is more particularly directed to a dual-chamber ICD, system and method wherein electrode configurations for ventricular arrhythmia termination and atrial arrhythmia termination are selectable from among a plurality of electrode configurations.
Implantable cardiac defibrillators (ICDs) are well known in the art. These devices, encapsulated in a conductive housing or enclosure, are generally implanted in the left pectoral region of a patient and electrically connected to the heart with one or more electrode-carrying leads. One lead includes at least one defibrillation electrode arranged to be positioned in the right ventricle. An arrhythmia detector detects ventricular arrhythmias, such as ventricular fibrillation. When such an arrhythmia is detected, a pulse generator delivers a defibrillating shock from the defibrillation electrode in the right ventricle to the conductive housing to terminate the arrhythmia. Alternatively, such arrhythmia terminating systems may further include another defibrillation electrode positioned in the right atrium and electrically connected to the conductive housing. In this arrangement, the defibrillating shock is delivered from the parallel connected right atrial electrode and the conductive housing to the right ventricular electrode.
Implantable atrial defibrillators are also known. These devices are also encapsulated in a conductive housing or enclosure and are electrically coupled to the heart by one or more electrode-carrying leads. The leads are known to include a defibrillation electrode positioned in the right atrium of the heart. When an arrhythmia detector detects an atrial arrhythmia, such as atrial fibrillation, an atrial defibrillating shock is then applied from the right atrial defibrillation electrode to the conductive housing.
Although not presently commercially available, combined implantable dual-chamber (atrial and ventricular) defibrillators continue to be investigated and under development. Because of the vast differences between ventricular and atrial arrhythmias, dual-chamber devices remain a challenge. For example, ventricular fibrillation is an immediately life threatening condition while atrial fibrillation, although uncomfortable and debilitating, is not a life threatening condition. Hence, there must be a preference for effective ventricular fibrillation treatment over atrial fibrillation treatment. Further, unless safety measures are taken in delivering atrial fibrillation terminating shocks, there is a potential for atrial fibrillation terminating shocks inducing ventricular fibrillation. Still further, by the time a ventricular fibrillation terminating shock is delivered, the patients are, in most occurrences, unconscious while, when atrial fibrillation terminating shocks are delivered, the patients are conscious and able to perceive discomfort from the atrial fibrillation termination shocks. Lastly, because of the relative locations of the atria and ventricles, the most effective ventricular fibrillation termination electrode configurations are different from the most effective atrial fibrillation termination electrode configurations.
Hence, in terms of arrhythmia termination, ventricular fibrillation termination electrode configurations must be those which provide the greatest assurance of successful arrhythmia termination. These configurations are those which exhibit the lowest ventricular defibrillation thresholds. In contrast, in arriving at an atrial fibrillation termination electrode configuration, consideration must be given to both atrial termination effectiveness and the degree of perceived discomfort by the patient to the delivered atrial arrhythmia termination shocks. The present invention addresses these issues.
The present invention provides an implantable cardiac stimulation system, device and method wherein atrial arrhythmia terminating pulses are confined to within the heart while ventricular arrhythmia terminating pulses may be delivered between a defibrillation electrode within the heart and another defibrillation electrode outside of the heart. With this arrangement, effectiveness of ventricular arrhythmia termination may be preserved while atrial arrhythmia termination may be achieved with minimized patient discomfort because the atrial termination pulse currents are confined within the heart and are precluded from recruiting the many pain neurons and skeletal muscle cells of the pectoral region.
In accordance with one embodiment of the present invention, the device and system delivers ventricular arrhythmia terminating pulses with an electrode configuration which includes the conductive housing encapsulating the device and delivers atrial arrhythmia termination pulses with an electrode configuration electrically independent of the conductive housing and thus confined to within the heart.
In accordance with another embodiment, a plurality of atrial arrhythmia terminating electrode configurations are available to the device, wherein each available atrial arrhythmia termination electrode configuration is electrically isolated from the conductive housing and thus confined to within the heart. One of the electrode configurations for atrial arrhythmia termination may be selected for use based upon a common arrhythmia termination characteristic, such as defibrillation energy threshold or perceived discomfort by the patient. The ventricular arrhythmia termination electrode configuration includes an electrode outside of the heart, such as the conductive device housing, to maintain ventricular arrhythmia termination effectiveness.
In accordance with a further aspect of the present invention, a preferred embodiment delivers a rounded, reduced-pain waveform for the atrial therapy as described in U.S. Pat. Nos. 5,906,633 and 5,830,236 which are incorporated herein by reference.
In accordance with a still further aspect of the present invention, a first plurality of electrode configurations are provided for ventricular arrhythmia termination, wherein at least one of the first plurality of electrode configurations includes the conductive device housing, and a second plurality of electrode configurations are provided for atrial arrhythmia termination, wherein each of the second plurality of electrode configurations is electrically isolated from the conductive device housing. A first electrode configuration from among the first plurality of electrode configurations may be selected for use based upon a common arrhythmia terminating characteristic, such as arrhythmia termination energy threshold. A second electrode configuration from among the second plurality of electrode configurations may be selected for use based upon a common arrhythmia termination characteristic such as arrhythmia termination energy threshold or perceived discomfort by the patient to the atrial arrhythmia termination pulses.
The cardiac stimulation device includes an electrode configuration selector, such as a switch, which selectively couples an atrial arrhythmia pulse generator to a pair of terminals which are coupled to the selected atrial arrhythmia termination electrode configuration and which selectively couples a ventricular arrhythmia termination pulse generator to a pair of terminals coupled to the selected ventricular arrhythmia termination electrode configuration.
As a result, by virtue of the present invention, ventricular arrhythmia termination effectiveness may be maintained while permitting flexibility in the selection of an atrial arrhythmia termination electrode configuration to achieve effective atrial arrhythmia termination with a minimum of perceived discomfort by the patient.